This invention relates to a passenger conveyor system, and more particularly to a drive machine that includes a drive belt to propel escalator tread plates.
A typical passenger conveyor, such as an escalator or moving walk, includes a frame, balustrades with movable handrails, tread plates, a drive system and a step chain for propelling the tread plates. The frame includes a truss section on both left and right hand sides of the frame. Each truss section has two end sections forming landings, connected by an inclined midsection. The upper landing usually houses the escalator drive system or machine positioned between the trusses.
The drive system of an escalator typically consists of a step chain, a step chain drive sprocket, an axle and a drive motor. The step chain travels a continuous, closed loop, running from one elevation to the other elevation, and back. The drive motor drives the chain, with the final drive commonly being a pair of toothed wheels located in a turn around area at the top of the escalator. The toothed wheels are based on tread plate size and are commonly of a 750 mm diameter for most escalator systems. The wheel drives the chain to which the tread plates are attached. Alternative approaches involve one or more machines located in the escalator incline. These machines also drive the step chain with a toothed wheel.
Escalators driven by a toothed wheel have some inherent vibration caused by a cogging effect associated with the discrete interface points between the teeth and the chain. Reducing the length of the links reduces the cogging effect, at the expense of increasing the cost of the step chain. Additional joints in the step chain also increase the stretch of the step chain as each joint wears.
The large drive wheels in the turn around also have a very large torque requirement. In order to maintain a reasonable machine size to produce this torque, multiple stages of gearing, and a chain reduction are needed. This can be costly and results in energy loss.
An escalator system designed according to this invention improves escalator operation by locating a belt drive machine within preexisting machine spaces under an escalator landing. The belt drive provides less cogging effect since the tooth spacing on the belt is much less than is practical with a chain.
The escalator drive machine includes a motor output sheave connected to a drive motor through a belt reduction assembly including a main output sheave. The main output sheave drives a small output sheave which drives the drive belt. The belt extends from the small output sheave and is guided along a plurality of guide sheaves located adjacent the step chain. A plurality of output belt teeth engage corresponding link teeth along the length of each step chain link. The guide sheaves are preferably located in parallel with a substantially straight length of links in the step chain. In one example, it has been determined that only 250 mm of engagement length between the belt and the links are required to transmit a load necessary to operate a common escalator system.
In addition, the drive belt can also drive the moving handrails of an escalator. By locating a pinch roller adjacent the handrail, the drive belt and handrail can be pinched together to provide a motive force to the handrail. The drive belt thereby synchronously drives the handrail.
In another embodiment the drive machine includes a counter-rotating motor which includes a wound motor primary and a motor secondary which rotate in opposite directions on a bearing stand. In this embodiment, the motor primary will engage a main sheave on one side of the escalator system using a first belt reduction assembly, while the motor secondary will engage another main sheave on the opposite side using a second belt reduction assembly which rotates in a direction opposite the first. This embodiment allows the use of the more efficient 6 pole counter-rotating motor which is approximately xc2xd the size of a common 12 pole motor.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.